This invention concerns the treatment of breast cancer or otherwise sited cancer, and an applicator capable of feeding back dose data during treatment. The invention also encompasses an efficient procedure for preparation of a radiation treatment plan, and verification and real-time control of treatment to plan following surgical tumor excision.
In treating cancer of the breast, as well as cancer found in other areas of the human body, with the patient under anesthesia, the tumor is surgically excised (with some surrounding tissue) and then typically, the surgical wound is closed and the patient is sent home pending determination of pathology of the excised tumor margins. The need for further excision is evaluated, and if necessary, carried out. A radiation treatment plan is then developed and the patient, in a series of later visits, is subjected to radiation treatment in the volume of tissue surrounding the excised tumor. This can often involve re-opening of the surgical cavity for insertion of an applicator for use with ionizing radiation sources, i.e. radioactive isotopes. The forming of a radiation treatment plan under these circumstances is usually a several-hour process that can require imaging of the excision cavity, to determine its shape and location in the body, using external devices such as magnetic resonance imaging or CT scanning equipment. Transfer of data is then needed between the imaging equipment and the treatment planning software for preparing a plan of irradiation, with the need to verify transferred data values to check for errors.
These several steps involve considerable time and associated costs and make intraoperative radiation treatment logistically difficult if not impossible. In the case of breast tumors, moving of the patient for imaging is a problem in itself, because the breast tissue is mobile and the excision cavity may move. There is a need for methodology which would allow intraoperative radiation treatment of breast cancer and other cancers, without moving the patient, without requiring external imaging devices and without waking the patient from anesthesia.
There is also a need for increased precision in delivering radiation to a volume of tissue following surgery, to closely follow a physician's prescription. For example, more versatility and accuracy are needed in avoiding damage to skin in irradiation of breast tissue, and avoiding damage to the heart, lungs and bones, while still delivering prescribed dosage where needed. Over-radiation of any tissue areas is to be avoided as much as possible.
The determination of a treatment plan depends on obtaining information on the shape and location of the excision cavity and the need to avoid damage to other areas of tissue (such as the skin, the chest wall, lungs and heart). Intraoperative radiation treatment has generally not been possible or practical for several reasons: the need to move the patient to the location of imaging equipment, to obtain the imaging data and transfer that data to a form useable in applicator equipment for performing the irradiation; and the need to obtain data on pathology of the excised tissue or the remaining tissue in the excision cavity, prior to executing a treatment plan. Obtaining these needed data requires considerable time; in general a patient following tumor excision should be ready for radiation treatment within about ½ hour, certainly less than 1 hour, and this is not possible with current procedures and equipment.
Current applicators comprise balloons with defined shapes, usually spherical, which can be filled to the appropriate size for the particular cavity, but beyond this size and shape, variation adjustment typically is not possible. The surgeon needs to cut as near-spherical an excision as possible to enable the proper use of the device. With the applicator in the excision cavity and filled, the patient's breast is imaged by exterior imaging equipment. This imaging not only determines the size of the inflated applicator within the breast excision cavity, but also enables the physician to look at any gaps between the applicator and the tissue at the boundaries of the excision cavity. Seroma from the wound may lie between the applicator and the cavity walls. 90% to 95% contact between the applicator and the excision cavity is required to ensure proper radiation delivery. If the applicator/tissue contact is sufficient, the physician uses a table to look up the needed dwell time for the diameter of the applicator and for the particular, known activity of the radio isotope source. The ionizing radiation source, i.e. an iridium (192Ir) wire on the end of a stainless steel guide wire, is inserted into the middle of the applicator for the prescribed duration. This works because the reference table for the source accounts for radiation intensity decay as a function of distance from the source location.
Proxima Therapeutics, Inc. has developed a procedure of this sort. The Proxima procedure is based on a known geometry, i.e. a spherical shape of the applicator and cavity. The equipment is not adaptable to an irregularly-shaped excision cavity. Moreover, the applicator and procedure are not useful for smaller-sized tumors, because of unacceptable surface-to-depth ratio of radiation dosage at near ranges of the radiation source.
In view of the above description of current methods, there is clearly a need for a system and applicator to facilitate expeditious creation of an ionizing radiation treatment plan, delivery of brachytherapy in accordance with that plan, and verification that such treatment was delivered, all in a manner to assure comfort and convenience to a patient. Further there is need for a system capable of post-excision treatment of small, early-stage cancers.